Hurricane Sandy — upgraded again Saturday just hours after forecasters said it had weakened to a tropical storm — headed north from the Caribbean and was expected to pummel the eastern United States.

The U.S. National Weather Service said the storm was expected to make landfall early Tuesday near the Delaware coast, then hit two winter weather systems as it moves inland, creating a hybrid monster storm that could bring torrential rain, high winds, and up to 2 feet of snow.

Even if Sandy loses strength and makes landfall as something less than a hurricane, the combined storm was expected to bring misery to a huge section of the eastern U.S. An 800-mile wide swath of the country could see 50 mph winds regardless of Sandy's strength.

Experts said the storm could be wider and stronger than Irene, which caused more than $15 billion in damage when it struck in August 2011, and could rival the worst East Coast storm on record.

On Saturday morning, forecasters said hurricane-force winds of 75 mph could be felt 100 miles away from Sandy's center.

Sandy killed more than 40 people in the Caribbean, wrecked homes and knocked down trees and power lines. On Saturday morning, the storm was about 335 miles southeast of Charleston, South Carolina. Its maximum sustained wind speed was about 75 mph.

Up and down the coast, people were cautioned to be prepared for days without electricity. Several governors, including Connecticut's Dannel Malloy and New Jersey's Chris Christie, declared states of emergency. And airlines said to expect cancellations and waived change fees for passengers who want to reschedule.

Mandatory evacuations were under way in southern New Jersey's barrier islands, which people were ordered to leave by Sunday afternoon, and Christie ordered the evacuation of all Atlantic City casinos and said state parks would close.

"We should not underestimate the impact of this storm and not assume the predictions will be wrong," Christie said during a storm briefing Saturday in North Midletown, near the coast. "We have to be prepared for the worst."

In North Carolina's Outer Banks, light rain was falling Saturday and winds were building up to a predicted 30 to 50 mph. Gov. Beverly Purdue declared a state of emergency for some coastal areas, and a steady stream of campers and other vehicles hauling boats left the low-lying islands for the mainland. Residents feared a temporary bridge built after Irene last year poked a new inlet through the island could be washed out again, severing the only road off Hatteras Island.

Jeff Masters, meteorology director of the forecasting service Weather Underground, said this storm could be as big, perhaps bigger, than the worst East Coast storm on record, a 1938 New England hurricane that is sometimes known as the Long Island Express, which killed nearly 800 people.

"It's looking like a very serious storm that could be historic," Masters said.

Sandy, having blown through Haiti and Cuba, continued to barrel north. A wintry storm was moving across the U.S. from the west, and frigid air was streaming south from Canada.

If the three weather systems meet Tuesday morning around New York or New Jersey, as forecasters predict, they could create a big, wet mess that settles over the nation's most heavily populated corridor and reaches as far west as Ohio.

With much of the U.S. East Coast in the storm's path, residents contemplated whether to heed the dire warnings.

"You know how many times they tell you, 'This is it, it's really coming and it's really the big one,' and then it turns out not to be?" said Alice Stockton-Rossini as she packed up to leave her home a few hundred yards from the ocean in Ship Bottom, New Jersey.

"I'm afraid people will tune it out because of all the false alarms before, and the one time you need to take it seriously, you won't. This one might be the one."

After Irene left millions without power, utilities were taking no chances and were lining up extra crews and tree-trimmers. Wind threatened to topple power lines, and trees that still have leaves could be weighed down by snow and fall over if the weight becomes too much.

New York City began precautions for an ominous but still uncertain forecast. No decision had been made on whether any of the city's public transportation outlets would be shut, despite predictions that a sudden shift of the storm's path could cause a storm surge of 3 to 6 feet (90 to 180 centimeters) and send water into the subway system.

The subway system was completely shuttered during Irene, the first such shutdown ever for weather-related reasons. Irene largely missed Manhattan but struck Brooklyn hard.

The storm loomed a little more than a week before Election Day, while several states were heavily involved in campaigning, canvassing and get-out-the-vote efforts. Republican presidential nominee Mitt Romney and Vice President Joe Biden both canceled weekend campaign events in coastal Virginia Beach, Virginia.

In North Carolina's Outer, retirees Larry and Jean Collier, of Brantford, Ontario, were leaving their beachfront hotel in Kill Devil Hills, North Carolina, early Saturday and trying to plot their route home knowing they risked driving into a mess.

"I'll try to split (the trip) right down the middle, not too close to Washington, not too far west," Larry Collier said. "The storm has kind of put a wrench in it."

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